As curable polyorganosiloxane compositions, a condensation reaction curable composition and an ultraviolet ray curable composition have been known.
The former condensation reaction curable polyorganosiloxane composition is a composition comprising polyorganosiloxane having a silanol group and an organosilicon compound having a hydrolyzable group which is to be cured with compounds such as tin compounds and titanium compounds (see, for example, JP-B-38-16798 and JP-B-40-21631 (the term "JP-B" as used herein refers to an "examined Japanese patent publication")). Such compositions are curable with moisture in the air at ordinary room temperature and are less subject to insufficient curing as encountered in addition reaction type compositions and, therefore, are used as a sealing material for construction, a coating material and a mold making material, a roll for copying machines, and so on.
These compositions, however, have a disadvantage in that they are unsuitable for use as adhesives for temporary fixation, i.e., for parts which are to be moved in a short time after fixation, although they are uniformly cured even in the inside thereof when allowed to stand for a long time because they are cured through permeation of moisture.
As ultraviolet ray-curable polyorganosiloxane compositions, (1) a composition in which various photosensitizers are added to a vinyl group-containing polyorganosiloxane composition and which is cured upon irradiation of high intensity ultraviolet rays (U.S. Pat. No. 3,726,710), (2) a composition comprising a mercapto group-containing polyorganosiloxane, polymethylvinylsiloxane and various peroxides (U.S. Pat. No. 3,816,282), (3) a composition comprising vinyl group-containing polyorganosiloxane, polyorganohydrodienesiloxane and a photosensitizer (JP-B-52-40334), (4) a composition comprising an acryl-based unsaturated group-containing polyorganosiloxane and a photosensitizer (JP-A-48-19682 (the term "JP-A" as used herein refers to a "published unexamined Japanese patent application")), and so on have been proposed.
These compositions are all instantly cured upon irradiation of ultraviolet rays, but have a disadvantage in that in the case of thick films, ultraviolet rays do not reach the inside thereof and thus areas where ultraviolet rays do not reach remain uncured.
For the purpose of overcoming the drawbacks of the above two types of compositions, as a composition having both condensation reaction curability and ultraviolet ray curability, a composition comprising a diorganopolysiloxane terminated a hydroxyl group at both ends thereof, a vinylsilane having a hydrolyzable group, organosiloxane having a mercapto group/ a curing catalyst and a photosensitizer has been proposed (JP-A-60-23176).
This composition, however, has disadvantages in that it has an unpleasant odor at the time of reaction which is characteristic of mercapto group-containing compounds, and when heat is applied, it converts metals into their sulfides.
In addition, a composition comprising an acryl. dialkoxysilyl or an acryl.diallyloxysilyl group-terminated polyorganosiloxane and a photosensitizer which contains a moisture curable catalyst has been proposed (JP-A-61127718, JP-A-61-276810). This composition, however, is poor in heat resistance and cold resistance, and is slow in rate of curing.